1. Field of the Invention
The present invention relates to a semiconductor device which has a circuit including a thin film transistor (hereinafter referred to as a TFT) and a method for manufacturing the semiconductor device. For example, the present invention relates to an electronic device which has as a component an electro-optical device typified by a liquid crystal display panel or a light emitting display device including an organic light emitting element.
Note that the term “semiconductor device” in this specification refers to a device in general that can operate by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all included in the semiconductor device.
2. Description of the Related Art
In recent years, attention has been focused on a technique for forming a thin film transistor (TFT) with the use of a semiconductor thin film (with a thickness of approximately several to several hundred nanometers) which is formed over a substrate having an insulating surface. The thin film transistor is widely applied to an electronic device such as an IC or an electro-optical device, and its development especially as a switching element of an image display device is rushed.
Various applications using such an image display device have been devised. In particular, application to a portable device has attracted attention. Currently, a glass substrate or a quartz substrate is often used; however, these substrates have the disadvantages of being fragile and heavy. Moreover, it is difficult to increase the size of a glass substrate or a quartz substrate, so that these substrates are unsuitable for mass production. Consequently, a TFT element is attempted to be formed over a substrate having flexibility, typically, a flexible plastic film.
Thus, several techniques have been proposed to peel an element formed over a glass substrate from the substrate and transfer the peeled element to another base material such as a plastic film.
The assignee of this application has proposed peeling and transferring techniques disclosed in References 1 and 2. Reference 1 discloses a peeling technique in which a silicon oxide film serving as a peeling layer is removed by wet etching. Reference 2 discloses a peeling technique in which a silicon film serving as a peeling layer is removed by dry etching.
In addition, the assignee of this application has proposed a peeling and transferring technique disclosed in Reference 3. Reference 3 discloses a peeling technique in which, when a metal layer (Ti, Al, Ta, W, Mo, Cu, Cr, Nd, Fe, Ni, Co, Ru, Rh, Pd, Os, Ir) is formed over a substrate and an oxide layer is stacked thereover, a metal oxide layer of the metal layer is formed at the interface between the metal layer and the oxide layer and this metal oxide layer is used for peeling in a later step.
[Reference 1] Japanese Published Patent Application No. H08-288522
[Reference 2] Japanese Published Patent Application No. H08-250745
[Reference 3] Japanese Published Patent Application No. 2003-174153